1. Field of the Invention
The present invention is broadly concerned with a greatly improved rotatable liquid-contacting device which can be used to give both aeration and liquid mixing, and, depending upon the direction of rotation thereof, the device can be used primarily as a miing unit, or, alternately, as an aerator. More particularly, it is concerned with such an aeration and mixing device which includes a flat, annular, rotatable plate provided with a plurality of radial, circumferentially spaced apart, outwardly projecting liquid-contacting elements which are especially designed and include leading and trailing faces presenting concavities.
2. Description of the Prior Art
One type of sewage treatment system presently in use includes a multiple-channel basin which is generally in the form of a plurality of circular or oval concentric channels and is designed for receiving raw, incoming sewage. A number of partially submerged spaced apart, specially designed aeration disks rotate in each channel in order to give enhanced mixing and aeration of the raw sewage. In such a system, the raw waste, after screening and grit removal, is fed directly into the first channel where it is dispersed in mixed liquor. The rotating aeration disks serve to mix and aerate the liquor and keep it moving in the channel. The mixed liquor makes a number of circuits of the channel depending upon the retention time required. A portion of the mixed liquor, approximately equal to the incoming and recirculated flow, is fed into succeeding channels through submerged transfer ports. After passing through the final inboard channel, the mixed liquor flows into a clarifier for final treatment.
In order to achieve optimum mixing and aeration of liquid sewage in a system of the type described, it is important that the rotating aeration disks be properly designed. For example, such disks normally include oppositely projecting elements on the opposed faces of the aeration disks which are designed to enhance both aeration and mixing. However, it will be readily seen that improperly designed liquid-contacting elements on the disks create undue resistance while not measurably enhancing aeration or mixing, with the result that increased horsepower demands are placed on the system, thereby increasing costs.
U.S. Pat. No. 3,744,774 is directed to a liquid aerating device in the form of a rotatable disk including protruding liquid-contacting formations on the opposed faces thereof. The liquid-contacting elements in this instance are basically pyramidal in shape, and include a sharp leading apex with a pair of diverging, flat faces terminating in a flattened, rearmost trailing face. It is believed that liquid-contacting elements of the type described in U.S. Pat. No. 3,744,774 are deficient in a number of important respects, including the aeration efficiency thereof and the degree of mixing obtainable when using the same. Accordingly, there is a real and heretofore unsatisfied need in the art for an improved disk-type aeration device which satisfies the competing demands of low horsepower requirements coupled with maximum aeration and mixing.